US2980861A

US2980861A - Switching systems

Info

Publication number: US2980861A
Application number: US680509A
Authority: US
Inventors: William J Popowsky
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1957-08-27
Filing date: 1957-08-27
Publication date: 1961-04-18
Anticipated expiration: 1978-04-18

Description

3 Sheets-Sheet 1 INVENTOR. WILLIAM J. POPOWSKY ATTORNEY.

Aprll 18, 1961 w. J. PoPowsKY swITcx-IING SYSTEMS Filed Aug. 27. 195'? N NN r April 18, 1961 Filed Aug. 27. 1957 W. J. POPOWSKY SWITCHING SYSTEMS 5 Sheets-Sheet 2 FIG. 2

INVENTOR. WlLLlAM J. POPOWSKY ATTORNEY.

April 18, 1961 w. J. PoPowsKY 2,980,861

SWITCHING SYSTEMS Filed Aug. 27, 1957 3 Sheets-Sheet 5 INVENTOR. WILLIAM J. POPOWSKY MMM ATTORNEY.

FIG. 3

recording, controllingA or` indicating instrument.

`2,980,1e61 swrrcrnNG SYSTEMS J. Popowsky, Wheaton, Md., assigner to Minne- ,apolls-Honeywell Regulator Company, a corporation Y of Delaware Filed Aug. 27, 1957, Ser. No. 680,509

- Claims. (Cl. S30-10) Thisinvention relates to electronic circuits, and more particularly to switching systems suitable for use in multiplex sampling of low-level signals.

" It frequently has been found desirable'to be able to switch between a plurality of low-level signals to applyV samples of those signals to the input of av single instrumentality. This is particularly true in the field of instrumentation where it is often desirable to be able to multiplex the signals from a plurality of primary sensing elements, such as thermocouples,y into the input of a single A These signals are most frequently direct current or voltage signals. Although Vthese signals have been Ysuccessfully switched by mechanical means, it is increasingly important that switching means involving no mechanical movements be provided. Here, too, electronic switching means have been provided, however, these switching means include systems wherein the signalV to be measured is passed throughY the switching tube. At the signal levels encountered in these circuits, considerable noise signals are introduced into the system and superimposed onto the data singals. To amplify the data signals prior to switch- -ing would require a separate ampliiier for each of the channels being sampled. When there are a number of such channelsbeing sampled, the expense of the separate amplifiers for each channel would be appreciable if not prohibitive. Y o

It is, accordingly, an object of this invention to provide an improved switching system suitable for use with low-level signals. o Y

\ It is another object of this invention vto provide an improved multiplexing system for low-level signals.

j' It is a further object of this invention to provide an improved switching system for low-level signals wherein switching is accomplished without the use ofV movable mechanical members.

It is a still further object of the present invention to provide an improved switching system for low-level signals wherein electronic switching means are employed, and wherein the data signal is not required to pass through the electronic switching tube. A It is yet another object of this invention to provide a switching system as set forth which features isolated inputs, that is, where there is no D.C. connection between the inputs ofthe system and the output. In accomplishing these and other objects, there has been provided,in accordance with the prent invention, an improved multiplexing means for low-level signals which includes magnetic modulator means for converting the signals` being sampled into alternating current signals, a diode gate for each sampled channel, and means for normally biasing the diode gate closed. An electronic switching tube circuit is employed to selectively and sequentially unbloclr the gate to permit the sampled signals to pass to an amplifier. I

A better understanding of this invention may be had @tsm rice

nection with the accompanying drawings, in which:

Fig. 1 is a schematic block diagram illustrating a system embodying the present invention;

Fig. 2 is a schematic circuit diagram showing details of one channel of the apparatus illustrated in Fig. l; and

Fig. 3 is a schematic circuit diagram showing details of an electronic switch such as may be used in the structure illustrated in Fig. 1.

Referring now to the drawings in more detail, there is shown in Fig. 1 a multiplexing system which includes a plurality of thermocouples 2, 4 and 6 which are representative of means providing low-level signal sources. Each of the thermocouples is connected to a corresponding magnetic modulator and

ilter circuit

8, 10 and 1.2, respectively. These magnetic modulator circuits may comprise magnetic modulators similar to those shown in the copending application of William A. Rote, Serial No. 470,097, tiled November 19, 1954, now Patent No. 2,- 882,352, granted April 14, 1959, and will be more fully explained hereinbelow. The magnetic modulator 8 is supplied with oscillatory carrier frequency excitation from an oscillator 14. Similarly, an oscillator 16 supplies ex- -citation to the modulator 10, and an oscillator 18 supplies excitation to the modulator l2. Although separate oscillators have been shown for each of the magnetic modulator units, it will be understood that a single oscillator may be coupled to supply excitation simultaneously to all of the modulators. The modulators convert the D.C. input signals into corresponding alternating signals, the amplitude and phase of which vary in accordance with the magnitude and direction of change in the input signals. The output of each of the magnetic modulators is fed to an electronic commutating arrangement 20. The electronic commutator sequentially and selectively connects the several outputs of the modulators to an amplifier 22, which includes means for demodulating the signal, reconverting it to a D.C. signal. The output of the amplifier is fed to a suitable utilization device 24 which may be a controller, a recorder or an indicator. The output of the amplifier is also connected in feedback relationship to all of the

magnetic modulators

8, 10 and 12. This feedback connection provides the usual D.C. stabilization for the D.C. amplification of the particular channel which is momentarily connectedthrough the commutator 20 to the amplifier 22. Although the'same feedback connection is made simultaneously to all of the modulators, it is of significance only in that channel which is connected, at the time, to the amplifier. o

In Fig. 2, there is shown a circuit diagram illustrating circuit elements which may bc used in the present invention as illustrated in block diagram in Fig. l. For purposes of simplicity of explanation, a single input channel is shown. However, since each of the other channels is identical with the illustrated channel, the showing of the additional channels is felt to be unnecessary for this description. r[he D.C. signal input may be connected to the input circuit terminals 26 and fed through a filter 28 to the input winding 30 of a magnetic modulator 32. The characteristic operation of the magnetic modulator is such that the output signal will be of a frequency which is the second harmonic of thefrequency of the exciting current. The filter 28 in the input circuit is tuned to this second harmonic frequency to prevent this signal from being reflected into the circuit of the primary sensing element connected to the terminals 26.

The magnetic modulator 32 is provided with an' exciting winding 34 which is energized through a transformer 36 from an oscillator 38. An output winding 40 is also provided for the magnetic modulator. The signal developed in the output winding 40 is applied to the Patented Apr. 18, 1961 3 input of a diode gate which includes the diode 42. Between the Winding 40 and the diode 42, there is positioned asignal limiter comprising the resistor 44, a coupling capacitork and the shunt connected diodes This i diode 42 is coupled to one of the plurality of cathodes 56v ofy the cold cathode counting tube 58, shown in Fig. 3. These counting tubes are characterized in that the conductive path is provided between the anode 60 thereof and a selected one of the plurality of cathodes. When properly triggered, the tube may be arranged to cause theV conductive path to proceed sequentially, on a predetermined time base, from one cathode to the next.

In Fig. 3, there is illustrated a suitable means for effecting the sequential triggering of the counting tube. This triggering means includes a pair of

electron tubes

62 and 64 connected in a circuit to constitute a monostable multivibrator. The dual output of the multivibrator is connected through

capacitors

66 and 68, respective-ly, to the control electrodes '70 and 72 of the counting tube 58. Although these

control electrodes

70 and 72 are schematically represented as being only'two in number, there are, in fact, two such electrodes for each of the cathodes 56. Since, however, corresponding ones of these electrodes are connected in parallel, the single schematic showing is sufficient for the purpose of this disclosure. The alternate keying of these control electrodes causes the conductive path in the tube 58 to step sequentially from cathode to cathode.

Referring to Figs. 2 and 3, it may be seen that the cur-` rent flow in the cathode circuit of the tube 58 causes a potenti-al to appear across the resistance network constituting the voltage divider 52. This potential is of a polarity opposite to the bias applied to the diode 42 and of a magnitude to neutralize the effect of such blocking bias and put a forward bias on diode 42. Thus, the current flow in the appropriate cathode circuit of the tube 58 unblocks the diode gate 42 allowing the signal developed by the output winding 40 to be applied to the amplifier circuit. As previously mentioned, in Figs.f2 and 3, there is illustrated but a single input circuit which is representative of the several circuits which may be connected in accordance with the present invention for selective sampling. features of the present invention isV to permit several input signals to be sequentially applied to the input of -a single amplifier. t The signal from the several input cir- -n wiii be-recaiied that one of the! cuits is applied at the junction 74 across the resistorV 76,

the connections to the other input circuits being represented by the arrow 78.

While all of the input circuits are premanently and directly connected to the. junction 74, only one at a time will be effective since only one gate will be unblocked by cur-rent flowing in the cathode circuits of the tube 58. These several input circuits are connected through the coupling capacitor 80 to the input of a first amplifier stage which comprises a dual triode 82 in which the corresponding electrodes are connected in parallel. This first stage is provided with a cathode'follower output taken across the cathode resistor 84 and applied to the grid of the next amplifier stage 86. The input to the amplifier 86 includes a tuned circuit consisting of an inductance coil 88 and a capacitor 90 which is arranged for the rejection of signals other than the second harmonic of the excitation energy applied to the magnetic modulator 32. The output of the amplifier 86 is capacitively coupled to the input of the power amplifier 92. A synchronous demodulator circuit is coupled to the output of the power stage 92 through a transformer 94.

A reference signal is obtained from the oscillator 38 for the synchronous operation of the demodulator. This signal is taken from the cathode circuit of the push-pull oscillator and constitutes a second harmonic of the fundamental frequency of the oscillator. This signal is applied through a. coupling capacitor 9X6 to the input of a two stage` amplifier 98. The demodulator includes the secondary windingy of the transformer 94, a pair of diode rectifers 102, anda pair of resistors 104. The reference signal from the amplifier 98 is applied through a load resistor 106 to the junctionl between the two resistors 104. Theoutput: of this demodulator is a D.C. signal, the polarity and magnitude of which is dependent upon the polarity and magnitude of the input signal applied to the magnetic modulator. This demodulated signal is applied in push-pull fashion; to the. input of a pair-ofv output D.C.; amplifiers 108 and.110, the output ing 1-14 on the magnetic modulator 32fto stabilize the operation of the circuit in the usual` manner of negative feedback applications.

In Fig. 3, the source of D.C. biaspotential 50 is illus.- .trated as comprising a transformer 116, the primary of which is ,coupled to an A.C. power supply. The secondary 118 of the transformer 116 is adjusted to give a suitable low voltage output. The output of the secondary is connected to a ldiode-bridge rectifier 120. The D.C. output of the bridge 120 isapplied through a filter 122 to the voltage divider 52.

yAs was previously noted, separate oscillators may be employed to supply the excitation to the individual magnetic modulators ora single oscillator may be appropriately coupled to supply the excitation for all of thev magnetic modulators. In the event that there are provided individual yoscillators for each of the magnetic modulators, then the-oscillators may be synchronized byv connectingV a synchronizing winding 124 onthe oscillator transformer 36 in parallel with the corresponding winding of the other several oscillators.

Thus, it may be seen that there has been provided an improved switching system suitable for multiplexing low-level signals 4wherein electronic Switching means are employed and without requiring that the data signals be passed through an electronicswitching tube and yet providing for the isolation .of the inputs.

What is claimed is:

1. An electronic switching system for llow-level signals comprising, in combination, a plurality of signal input circuits, a magnetic modulating means coupled to each of said input circuits for modulating input signals: in accordance with a modulator exciter frequency, an output amplifier, means providing a coupling path between each of said modulating means and said output amplifier, control means in.. each Vof said paths, each of said control means including a diode and meansfornormally biasing said diodes to block the'passagek of signals in said paths, an electronic counting .tube having ananode and a plurality of cathodes, means for energizing said `counting tube to develop a conductivepath between said anode and o ne of said cathodes, and means ,forV shifting ,saidV conductive path sequentially frlomcathode to cathode, each of said control means being ,coupledk to the cathode circint of a separate one of s-aid cathodes of said counting tube whereby to modify ,the bias condition on said control means selectively and sequentially in accordance with the position `of said conductive path in `said counting tube to unblock correspondingiones-of said paths.

2.Y An electronic switching system for low-level signals comprising, in combination, a plurality of signalinput circuits, va magnetic modulating means coupled to each of said inputcircuits, for modulating input signals in accordance with a modulator exciter frequency, said modulating means comprising a magnetic core structure having thereon a balanced pair of exciting windings, an input winding and an output Winding, an output amplifier, means providing a coupling pathv between each of said output windings and said ampliiier, control means in each of said paths, each of said control means including a diode and means for normally biasing said diode to block the passage of signals in said paths, an electronic counting tube having an anode and a plurality of cathodes, means for energizing said counting tube to develop a conductive path between said anode and one of said cathodes, and means for shifting said conductive path sequentially from cathode to cathode, each of said control means being coupled to the cathode circuit of a separate one of said cathodes of said counting tube whereby to modify the bias condition on said control means selectively and sequentially in accordance with the position of said conductive path in said counting tube to unblock corresponding ones of said paths.

3. An electronic switching system for low-level signals comprising, in combination, a plurality of signal input circuits, a magnetic modulating means coupled to each of said input circuits for modulating input signals in accordance with a modulator exciter frequency, an output amplifier, means providing a coupling path between each of said modulating means and said output amplifier, control means in each of said paths, each of said control means including a diode and means for normally biasing said diodes to block the passage of signals in said paths, an electronic counting tube having an anode and a plurality of cathodes, means for energizing said counting tube to develop a conductive path between said anode and one of said cathodes, means for shifting said conductive path from cathode to cathode, each of said control means being coupled to the cathode circuit of a separate one of said cathodes of said counting tube Whereby to modify the bias condition on ysaid control means selectively and sequentially in accordance with the position of said conductive path in said counting tube to unblock corresponding ones of said paths, and demodulating means coupled to the output of said amplifier to provide demodulated output signals which are representative of the input signals.

4. An electronic switching system for low-level signals comprising, in combination, a plurality of signal input circuits, a magnetic modulating means coupled to each of said input circuits for modulating input signals in accordance with a modulator exciter frequency, said modulating means comprising a magnetic core structure having thereon a balanced pair of exciting windings, an input winding and an output winding, an output ampliiier, means providing a coupling path between each of said output windings and said amplilier, control means in each of said paths, each of said control means including a diode and means for normally biasing said diode to block the passage of signals in said paths, an electronic counting 6 tube having an anode and a plurality of cathodes, means for energizing said counting tube to develop a conductive path between said anode and one of said cathodes, means for shifting said conductive path sequentially from cathode to cathode, each of said control means being coupled to the cathode circuitof a separate one of said cathodes of said counting tube whereby to modify the bias condition on said rcontrol means selectively and sequentially in accordance with the position of said conductive path in said counting tube to unblock corresponding ones of said paths, and a synchronous demodulating means coupled to the output of said amplifier to provide demodulated oultput signals which are representative of the input signa s.

5. An electronic switching system for low-level signals comprising, in combination, Ka plurality of signal input circuits, a magnetic modulating means coupled to each of said input circuits for modulating input signals in accordance with a modulator exciter frequency, said modulating means comprising a magnetic core structure having thereon a balanced pair of exciting windings, an input winding, an output winding and a feedback winding, an output amplifier, means providing a coupling path between each of said output windings and said amplifier, control means in each of said paths, each of said control means including a diode and means for normally biasing said diode to block the passage of signals in said paths, an electronic counting tube having an lanode and a plurality of cathodes, means for energizing said counting tube to develop a conductive path between said anode and one of said cathodes, means for shifting said conductive path sequentially from cathode to cathode, each of said control means being coupled to the cathode circuit of a separate one of said cathodes of said counting tube whereby to modify the bias condition on said control means selectively and sequentially in accordance with the position of said conductive path in said counting tube to unrblock corresponding ones of said paths, a synchronous demodulating means coupled to the output of said amplifier to provide demodulated output signals which are representative of the input signal, and means coupling said output signals in negative feedback relationship to said feedback Winding on all of said modulating means.

References Cited in the le of this patent UNITED STATES PATENTS 1,847,079 Burton Mar. 1, 1932 2,297,543 Eberhardt et al. Sept. 29, 1942 2,444,726 Bussey July 6, 1948 2,485,343 Zuschlag Oct. 1S, 1949 2,568,779 Veaux Sept. 25, 1951 2,697,746 Kennedy Dec. 2l, 1954 2,723,307 Baracket et al. Nov. 8, 1955 2,773,982 Trousdale Dec. ll, 1956 2,806,175 Hansen Sept. l0, l957